Citrus fruits, e.g. oranges, lemons, limes, etc., consist of an endocarp containing the juice sacs and seeds, a mesocarp of white, pulpy material commonly called the albedo and an exocarp, commonly called the flavedo, which contains the essential peel oil sacs and the plastids which contain color bodies. In immature fruit, the plastids are referred to as chloroplasts because they contain relatively large amounts of chlorophyll and relatively small amounts of carotenoid pigments, and, therefore, give the fruit a green color. As the fruit matures, the amount of chlorophyll decreases and the amount of carotenoids increases to ultimately give the fruit its characteristic ripe color. The plastids in such mature fruits are referred to as chromoplasts.
The carotenoid pigments present in the flavedo chromoplasts potentially have many commercial uses, especially if they could be isolated in a concentrated form in the essential peel oil. For example, juices extracted from early season fruit often have poor coloring and, after concentration, reduced flavor. These deficiencies could be remedied by adding a highly colored essential peel oil to improve color and enhance the flavor of these juices. Further, such highly colored peel oils have many potential commercial uses as colorants and flavoring materials in other food products.
The prior art teaches a variety of ways for extracting peel oil from oranges, both by mechanical and by chemical means. Several mechanical devices for extracting essential peel oil from fruit have been developed ["Florida Citrus Oils", Kesterson, et al., Technical Bulletin 749, December 1971, pp 15-20]. In one device, blades cut into the flavedo while simultaneously squeezing the fruit in order to press out the juice and rupture the peel oil sacs. The released oil, along with pieces of peel, is then washed away with a water spray to be recovered later by centrifugation. In another device, stainless steel cylinders which have sharp pointed projections are rotated on a shaft, and, as the fruit passes over them, the oil is released by the piercing action. A mist of water washes the oil from the fruit, and the resulting oil and water mixture is collected in a pan below the cylinders to be subsequently clarified by centrifugation. In yet another device, peel cups or quarters from juice extractors are fed into an extractor where a knife blade splits the peel into flat pieces of albedo and flavedo. The flavedo slice is given a knurled roll pressing in the presence of water to release and transfer its oil to the water. Separation of the oil-water mixture from the flavedo is then made with a paddle finisher.
The extractors described above provide fast and efficient methods of obtaining peel oil from oranges. However, because of their inherent requirements for water sprays to facilitate oil removal, water soluble flavoring components in the oil, such as decanal and linalool, are lost during processing. In addition the oils recovered by these methods are generally low in carotenoids due to insufficient contact time of the released oil with the chromoplasts in the spent flavedo. The levels of carotenoid pigments present in oils extracted as described above are so low that addition of even the maximum allowable amount of such oils to food products does not significantly affect their color. Thus such mechanical extraction, while efficient for peel oil, is inefficient for peel carotenoids.
The prior art also teaches solvent extraction of the carotenoids remaining in the spent flavedo. In the "Proceedings of the Florida State Horticultural Society," volume 81, pages 264-268 (1968), Ting and Hendrickson disclose a method whereby the peel carotenoids are extracted from ground flavedo with acetone, and, in Food Technology, volume 23, pages 87-90 (1969), Ting and Hendrickson disclose an improvement on the above-described process which comprises diluting the acetone extracts with water, extracting the carotenoids from the aqueous acetone solution with hexane, and purifying the carotenoids by column chromatography.
Kew and Berry [Journal of Food Science, 35, pp. 436-439 (1970)] disclose a method in which spent flavedo is finely ground in the presence of n-hexane. The carotenoid-containing hexane solution is isolated from the peel particles and partially concentrated. After further treatment of the carotenoid solution with methanolic potassium hydroxide and subsequent steam distillation, the hexane extract is concentrated by evaporation.
While the aforementioned methods provide efficient means of extracting carotenoid pigments from orange flavedo, the use of solvents precludes the use of such pigments in foods under the food laws of many countries. In addition, the final products obtained are devoid of most or all of the volatile flavoring components by virtue of the concentration steps.
From the foregoing discussion of prior art practices, it does not appear that an efficient process has been developed for the production of an essential peel oil which contains both the volatile flavoring components and a high concentration of the carotenoid pigments found in the flavedo chromoplasts.